1. Field of the Invention
The invention relates to a process for stacking and diluting paper fiber stock which is stacked in a high-consistency condition in a first volume during a defined dwell time and subsequently conveyed to a second volume which adjoins downstream the first volume, in which the paper stock is diluted at least until it is pumpable and is drawn off as a suspension through a wire. The second volume generates a circulation flow that carries away the high-consistency paper fiber stock located on the edge of the first volume, dilutes it and conveys it to a wire, which is kept clear by a rotating rotor.
2. Discussion of Background Information
Methods of this type are used to stack paper fiber stock which has already been disintegrated and has a dry matter content of, e.g., between about 20 and about 40%, such that it remains in this condition for a desired dwell time in order, e.g., to store the fiber stock or to allow a chemical reaction to occur. As a rule, a container is used to hold the paper fiber stock. It is known that for many chemical reactions a minimum dwell time is necessary, whereby there are also cases in which it is essential not to exceed or fall below the dwell time, where it must therefore lie within a certain range. A typical application is bleaching high-consistency paper fiber stock. In principle, a higher consistency is aimed at there, firstly so as to keep the required volume as small as possible, and secondly to promote the effectiveness of the chemical reaction. As a rule, a temperature is set at considerably higher than the surroundings.
In most cases the paper fiber stock in the stacking consistency is not pumpable, which makes it more difficult to handle. For this reason, after the completion of the chemical reaction the paper fiber stock is diluted at least enough to make it pumpable. This dilution often takes place outside the container, as dilution inside the container can lead to problems of operating reliability.
A method is known from German Patent Application No. DE 198 26 879 A1 with which the above-mentioned dilution also takes place inside the stacking container. The known method is particularly effective when two different rotors interact in the dilution area of the container. However, this additional expenditure is not possible or useful in every case. In many cases there is not enough room for the second drive, either.
German Patent Application No. DE OS 35 22 395 C1 shows a storage container (tower) for recovered paper. This is used for the chemical treatment of contaminated recovered paper that has not disintegrated. The method is therefore aimed at initially pretreating the raw material accumulated as recovered paper chemically and in a high-consistency condition so that it can subsequently be processed with a slushing rotor arranged in the base of the container. The described storage tank and the slushing rotor are thereby adjusted to and appropriately developed for the raw material that is not disintegrated and therefore yet to be disintegrated.
European Patent Application No. EP 0 475 669 B1 shows a stacking container in the base of which a dilution takes place by means of the addition of water and mixing with the aid of a propeller. Although this process makes it possible to produce a pumpable suspension, it is very nonuniform, so that, e.g., it is proposed to place pumps at different points, which tolerate the different consistencies of the suspension.